Microbiology

Microbiology Study Guide

Chapter 4: Disease, Resistance, and the Immune System

Objectives 1. Understand the host-parasite relationship. 2. Describe the progress, different types, and establishment of diseases. 3. Differentiate between mechanical and chemical factors, including inflammation, phagocytosis, and individual, racial, and species immunities as the non-specific resistance to diseases. 4. Understand antigens and the immune system. 5. Determine the types of immunity, and serological and diagnostic reactions. 6. Classify various disorders of immunity. The Concepts of Infection and Disease There is a strong association between bodily defenses and pathogenic diseases. When these defenses are able to resist pathogens, the body remains in a healthy and fit state. But if these pathogens overcome the bodily defenses, one is likely to suffer from diseases and infections. The consequences of diseases are loss of health, likely damage on short-term or long-term health, and even death in extreme cases. The outcome of the disease is dependent on the nature and magnitude of the disease. Derived from the Greek word “pathos,” meaning suffering, pathology is described as the scientific study of disease. The cause of the disease is studied in the field called etiology . The agent that carries and spreads disease is known as an etiologic agent. The structural and functional changes in body tissues due to the occurrence of disease are studied in a field called pathology. It is important to understand the basic difference between infection and disease. Infection is caused when microorganisms invade the tissues of the body. Disease, on the other hand, leads to diversion from the condition of good health due to the impact caused by the microorganisms residing in bodily tissues. Normal Flora When tissues of the body are exposed to the external environment, the population of microorganisms exists and is termed as normal flora. This normal flora can either be permanent or temporary. The temporary flora is concerned with the presence of flora for a short time period because it disappears later. When normal flora and body tissues live together, it is referred to as symbiosis . When the relationship between the normal flora and the body appear to exist where one benefits while the other remains 4.1 The Disease Process Host-Parasite Relationships

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